Yaw inertias for fixed-bottom

[gbarter]

Purpose

Fix error in zero-value for PtfmYIner when doing fixed-bottom and improve value for NacYIner per Roger Bergua's advice.

Roger recommends a dummy value (at least 1e4) for PtfmYIner and adding 1/3 of the tower yaw inertia to the NacYIner value as an activated lumped modal mass.

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

• I have run existing tests which pass locally with my changes
• I have added new tests or examples that prove my fix is effective or that my feature works
• I have added necessary documentation

[gbarter]

Matching IEA 15 PR

[gbarter]

Also fixes this Issue

[dzalkind]

I had to increase the dummy value of PtfmYIner to get OpenFAST to run locally. 1e7 was the lowest value that worked for me. Thanks for doing this!